The major objective is to determine the appropriateness and the limitations of the Mongolian gerbil as an animal model of presbyacusis. This is achieved, in part, by monitoring some of the properties of auditory electrical potentials recorded from awake and sedated animals who have been born and reared in an acoustically controlled environment. Of especial interest are auditory potentials arising from the auditory nerve and brainstem and their age-related declines as indicated by auditory sensitivity, amplitude-intensity and latency-intensity functions, and measures of frequency selectivity. A second objective is to assess interactions between hearing loss associated with aging and the hearing loss produced by exposure to low and moderate levels of noise. Noise levels range from 65 to 98 dBA, and exposure durations from 10 days to 2.5 yrs. Of specific interest is the determination of the relations between the magnitude of the hearing loss and the level of the noise for short-duration exposures, long-duration exposures which occur prior to the onset of aging effects, and long-duration exposures where age- related interactions occur. Animals from this project are the experimental animals of Project #3, 4 and 5 on cochlear pathophysiology, histopathology, and histochemistry. Results of the proposed experiments are pertinent to diagnostic and rehabilitative procedures in noise-induced hearing loss and presbyacusis as well to theoretical issues in audition and in the neurosciences.